Electric current rectifier control



Nov. 7, 1933.

E. KERN ELECTRIC CURRENT RECTIFIER CONTROL Filed April 28, 1932 1 1// 11, I //////1 11/;1/ 1 /1 I III/III! Patented Nov. 7, 1933 PATENT OFFICEELECTRICCURRENT RECTIFIER CONTROL Erwin Kern, Ennetbaden, Switzerland,assignor to Aktiengesellschaft' Brown Boveri & Cie, Baden, Switzerland,a joint-stock company of Switzerland Application April 28, 1932, SerialNo. 608,012, and

" in Germany May 2, 1932 3 Claims. (Cl. 175-354) This invention relatesto improvements in electric current rectifiers of the metallic vapor arctype and more particularly to means associated with the anodes of suchrectifiers by which the arc flowing therein may be controlled.

Electric current rectifiers may be used as circuit interrupters, inconnection with condensers, for the disconnection of short circuits inhigh voltage direct current systems in which the use of quick actingswitches is impractical due to problemsof construction of such. switcheswhich have not yet been solved. The ignition vol ge for the anodes of arectifier or the voltage which must be im-.

pressed upon one of several anodes when it is desired that such anodepick up the are within a rectifier, is generally controlled by gridsarranged between the anodes and the cathode of a rectifier. To securethe best operation of such grids, it is necessary that the grids have.the maximumsurface area without being so constructed as tomaterially-decrease the free crosssection area of the are guides whichpartially enclose the anodes and Withinwhich the grids are arranged andsupported. The above requirements for the construction of the grids aremet by grids in which the greatest portion of the total surface areaextends substantially coaxially with the are guides or in which aplurality of grids arranged over each other in each of the are guideshave relatively small areas at right angles to the axis of the arcguide. 1

When a plurality of grids are arranged within each arc guide dependentfrom the anodes of a rectifier, contacting of the arc with the metallicportions of the structure may cause the formation of a cathode spotwhich is probably due to the action of the arcon and the potentialdifierence's of the several portions along the axis of the are guide.Formation of such cathode spots leads to unstable conditions in the arcand may cause the occurrence of over-voltages in the rectifier due torapid changes in the arc drop. Such spots are formed particularly whenthe grids block a large portion of the area ofthe space enclosed by theare guides.

I All grid constructions cause an increase in the voltage required 'tocause the arc to be picked up' by an anode. When grid structures capableof interrupting the are are used, the resultant increase in ignitionvoltage is so great that picking up of the are by an anode becomes verydifilcult which is occupied by the grids by which move- -ment of the arecarrying electrons toward the anode may be accelerated. The use of aplurality of grids in an arc guide so increases the arc drop from theanodes to the cathode that the formation of cathode spots on the areguides is undesirably facilitated and the grids cannot perform theirfunction for the reason that they are enclosed within the thenconductive arc guide.

It isjt-herefore, an object of the present invention to provide a gridcontrol system for electric current rectifiers in which a plurality ofgrids are arranged over each other within are guides partially enclosingthe anodes.

Another object of the invention is to provide a grid control system forelectric current rectifiers in which a plurality of grids, arranged overeach other within the anode are guides and insulated from each other andfrom the guide, are supplied with different voltages from a commonsource.

Another object of the invention is to provide a grid control system forelectric current rectifiers in whicha plurality of grids, arrangedadjacent each anode within the path of the arc flowing therefrom, aresupplied with voltage from a single source in such manner that apotential drop is present between the several grids and between theanode and the grid nearest thereto.

Another object of the invention is to provide a gridcontrol system" inwhich a plurality of grids are supplied with voltage from a singlesource in such manner as to produce a gradually increasing potentialdrop fromthe anode to the cathode when the rectifier is in operation andin the opposite direction when the rectifier is not in operation.

Another object of the invention is to provide a control grid structurefor electric current rectifiersin which a plurality of grids are soarranged over each other within the are guides as to partially cover theinner surface of the guides.

Another object of the invention is to provide a control gridconstruction for electric current rectifiers in which a'plurality ofgrids extend partures embodying the present invention and showing theconnections for applying potential from a common source to the severalportions of such structure, and

Fig. 2 is an enlarged vertical sectional view of a multiple grid orinner arc guide structure embodying the invention and shown associatedwith one of the anodes of a rectifier as indicated diagrammatically inFig. 1.

Referring more particularly to the drawing by characters of reference,the reference numeral 3 designates a container or tank having a pool ofvaporizable material 4, such as mercury, in the bottom thereof to form acathode. A plurality of anodes 6 are arranged to extend into the tankthrough insulators 7 and are partially enclosed by outer guides 8 andinner guide constructions to be described in detail hereinafter, for anarc which is to be picked up by the anodes from excitation anodes (notshown) and which arc flows from the anodes to the cathode during normaloperation of the device as is usual in electric current rectiflers ofthe metallic vapor arcing type. The anodes are supplied with electriccurrent from a transformer connected with a suitable source ofalternating current (not shown), the secondary winding of thetransformer only being indicated at 10. The neutral point of thetransformer secondary winding 10 has connected therewith a conductor 11.The conductor 11 in combination with a conductor 12, connected with thecathode 4, forms a direct current output circuit for the supply ofdirect current consuming devices as indicated at 13.

An inner arc guide structure is arranged within and supported from theouter arc guide 8. The inner guide is composed of a shield or guidemember 16 arranged about the anode head and resting on one set of aplurality of sets of insulators 17 secured in the outer arc guide and aplurality of tubular members 18, 19 and 20 spaced from the outer arcguide and supported by adjacent sets of insulators 1'7 respectively. Theends of the tubular members 18, 19 and 20 are formed with difierentdiameters to permit adjacent ends of separate members to overlap eachother in spaced parallel relation. Thus each tubular member is supportedon one set of insulators 17 and is spaced from the outer arc guide 8 insuch manner as to be coaxial therewith and to be retained in spacedrelation from the other tubular members by a second vset of insulators17 which supports another of the tubular members. The bottom of theouter arc guide 8 is partially closed by a member 22 which shields thesets of insulators from damaging contact with the arc during operationofthe rectiher. A control electrode or grid 24 is mounted within the innershield 16 in either conductive or insulated relation therewith as may bedesired.

The construction of the inner arc guide is thus such that the entireinner guide structure is insulated from the anode and that the severalportions thereof are insulated and retained in spaced relation from eachother. Annular spaces are thus left free, except for the space occupiedby the sets of insualtors 17, between the several inner guide portionsand between the inner and outer arc guide structures. The parallelextending surfaces of the inner arc guide structure absorb theelectrostatic field set up by the arc passing therethrough. The voltagedrop which otherwise is present upon passage of the arc through suchspaces is thus avoided. The are cannot therefore flow from the inner tothe outer guide nor vice-versa and the formation of cathode spots on theare guides is avoided. To obtain the best results, the annular spacesbetween the two are guide structures should be kept as narrow aspossible. The several portions forming the inner arc guide structurecannot be metallically connected and must be either insulated from theouter arc guide or connected therewith through ohmic resistance. If itis considered undesirable to extend a plurality of conductors throughthe arc guide, the tubular members 18, 19 and 20 need not have apotential impressed thereon and may then be made of insulating material.The inner arc guide construction then serves merely as a shield toprevent impingement of ionized vapor on the outer arc guide and thusprevents the formation of cathode spots.

When the tubular members 18, 19 and 20 are made of conductive material,and, together with the cathode 4 are connected with a source ofpotential as will be hereinafter described, a potential may be impressedon the control electrode or grid 24 and on the tubular members 18, 19and 20 from different points of a resistance 26, the one end of which isconnected with the positive bus bar 12 of the direct current outputcircuit. The other end of the resistance 26 may be con nected by meansof a switch 27 with either the positive or the negative pole of a sourceof electric curernt 28. A resistance 29 is connected across theterminals of the voltage source 28 and is tapped at the mid pointthereof to the positive bus bar 12.

When an anode 6 is to pick up the arc from an excitation anode (notshown), the switch 2'? is connected with the positive terminal of thesource of current 28. The grid 24 and the tubular members 18, 19 and 20then have a potential impressed thereon which is positive with respectto the cathode and the impressed potentials are different, the potentialof each portion of the structure being that of the resistance 26 at thepoint of connection therewith of the several portions of the structure.The potential drop from one of the portions to the other may thus becontrolled by changing the location of the conhection of the severalportions with the resistance 26 and may be made large enough to secureproper ionization within the space occupied by the inner arc guidestructure within the outer arc guide structure. Thus grid 24 is positiverelative to tubular member 18, tubular member 18 is positive relative totubular member 19, tubular member 19 is positive relative to tubularmember 20, and tubular member 20 is positive relative to the potentialof the cathode 4. Picking up of the are by the anode 6 is thusfacilitated because the speed of the ions within the arc guide isaccelerated.

When an arc is to be prevented from attaching on any of the anodes 6,the switch 27 is placed on the negative pole of the current source 28which causes the tubular member 20 to become negatve relative to thepotential of the cathode 4, the tubular member 19 becomes negativerelative to the potential of the tubular member 20, the tubular member18 becomes negative relative to the tubular member 19, the grid 24becomes negative relative to the potential of the tubular member 18. Thepotential difference between the several tubular members and the gridstructure thus causes a braking action on such electrons as arepermitted to pass through the member 22.

The arrangement of the several portions of the inner arc guide over eachother has the great advantage, over a single member constructed withinthe outer arc guide 8, that the occurrence of a cathode spot on theinner arc guide structural portions is avoided because the currentsupplied thereto must flow over resistance 26 which limits the currentto a low value. The danger of the occurrence of a cathode spot on thearc guide 8 is minimized by the use of the shield 16 which partiallysurrounds the anode 6 and by the tubular members which overlap eachother and the shield 16 thus causing an overlapping electrical action aswell as an overlapping mechanical action on the vapor entering throughthe aperture in the member 22. Suflicient barriers are thus provided toprevent the flow of the electrons to the arc guide structure 8. Thefurther advantage is also obtained from such construction that theinsulators on which the shield 16 and the tubular members 18, 19 and 20are supported from the outer arc guide 8 are protected from the actionof the arc flowing from the anode 6 and may, therefore, be made muchsimpler and lighter than heretofore. Slight leakages of metallic vaporthrough apertures in the arc guide 8 such as at the point of attachmenttherewith of the inner arc guide structure supporting insulators andabout the insulating bushing for the connection of the several portionsof the inner arc guide structure with the resistance 26 will not permitan arc to flow therethrough due to the mechanical shielding action ofthe inner arc guide structure.

Although but one embodiment of the present invention has beenillustrated and described, it will be apparent to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

It is claimed and desired to secure by Letters Patent:

rality of members arranged over each other within each outer arc guideand insulated therefrom, a source of potential supply, means forimpressing a different potential upon each of the said membars from saidsource of supply to secure a gradually changing potential drop from theanodes to the cathode, and means for reversing the direction of thepotential drop over said members.

2. In a. system for controlling the action of an are within an electriccurrent rectifier of the vapor type having anodes, a vaporizable cathodeand outer are guides partially enclosing the anodes; inner arc guidestructures including a plurality of members arranged over each otherwithin each arc guide and insulated therefrom, a source of potentialsupply connected with and common to all of said members, a resistancecapable of connection at one end thereof with said source, the other'end of said resistance being connected with the cathode of therectifier, each of said members being connected with said resistance ata different point thereof, and a switch for changing the connection ofsaid resistance with said source from one pole to the other polethereof.

3. In system for controlling the action of an arc wit an electriccurrent rectifier of the vapor type having anodes, a vaporizable cathodeand outer are guides partially enclosing the enodes; inner arc guidestructures including a plurality of members arranged over each otherwithin each outer arc guide, a single source of potential supplyconnected with said members, a resistance bridging said source, themid-point of said resistance being connected with the cathode of therectifier, a resistance capable of connection at one end thereof withsaid source, the other end of said resistance being connected with thecathode of the rectifier, each of said members being connected with saidsecond mentioned resistance 'at a different point thereof, and a switchfor changing the connection of said second mentioned resistance withsaid source from one pole to the other pole thereof.

ERWIN KERN.

